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My aim is to simulate a thruster plume (with CEX and electrons) on a floating spacecraft with active surfaces current collection in a very low density environment plasma (interplanetary trip) that would be equivalent of vacuum.
In the past the thruster ion plume was usually neutralized (in term of plasma potential) by implementing a background electron population, and it worked fine. However with a floating spacecraft, this unphysical plasma will false the current collection.
In order to achieve my goal, the only solution to my knowledge (i'm a SPIS newbie) is to implement an electron source ejecting a given current. I tried that, either with a dedicated source or by combining ions and electrons sources on the same active surface. After tweaking a lot the time steps and mesh size i still cannot get a physical plume potential. It goes up to 8000V a few cm above the thruster plane.
Does someone have any advice, link of past studies/attempt or contact that could help me ?

I'm aware that plume neutralization is a hot topic in SPIS, but since i don't care about the physical processes behind the neutralization but just want to cancel the space charges in the vicinity of the thruster i think it should be achievable.